/usr/bin/cpp is henceforth deprecated in MirOS-current as well as
in MirOS-stable; it’s a shell script (overhead!) to call either mcpp(1) or
Reiser CCCP. It will be removed in MirOS-current ASAP.

/usr/bin/mcpp calls GNU cpp directly. Its manual page used to be
called cpp(1) and is now called mcpp(1). Since we are going towards a multi
compiler system, people are expected to use “${CC} -E” as C Præprocessor in
the future, instead of relying on an external cpp binary, when compiling. A
cpp binary will still be provided for the X(7) Windowing System and similar
uses. /usr/bin/mcpp will be removed some time before MirOS #11

/usr/libexec/cpp used to be Reiser CCCP without a manual page.
It is now pcc cpp(1) with a manual page.

ahoka@ came up with the idea of using the (much faster) pcc cpp over the
(rather slow) GNU cpp for purposes like Xresources, xdm configuration files,
etc. Reiser CCCP could be used too, but it’s lacking in terms of standards
and features. However, pcc cpp is under the Caldera licence, and thus, the
following text must be reproduced in this announcement. (It’s still much
more free than GNU cpp.)

This product includes software developed or
owned by Caldera International, Inc.

Technical issues: pcc cpp uses getopt(3) and, as such, has a command line
syntax which is totally different from the CPP standard. It also
pre-defines neither any macros nor include paths. Be warned, and
expect some breakage until everything is sorted out.